Outer Helmholtz Plane Regulation and In Situ Zn Surface Reconstruction for Highly Reversible Zn Anodes

Abstract Metallic Zn, a promising anode for aqueous energy storage devices, suffers from uncontrolled dendrite growth and corrosion, leading to a short cycle life and low Coulombic efficiency (CE) in Zn‐based batteries. Herein, a composite electrolyte including zinc sulfate, copper(II) chloride, and poly( N ‐diallyldimethylammonium chloride) (PDADMAC), denoted as PDADMAC–CuCl 2 –ZnSO 4 , is applied to simultaneously reconstruct the outer Helmholtz plane (OHP) and homogenize the Zn surface for highly reversible Zn anodes. The results of characterization, namely Raman spectroscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, density functional theory calculations, and electrochemical tests, confirm that the addition of chloride ions promotes the adsorption of PDADMAC on the OHP of the electric double layer and controls the Zn deposition process by regulating the electric field. Simultaneously, in situ Zn surface homogenization is accomplished by the reaction of Cu 2+ on the Zn surface. As a result, the highly reversible Zn anode sustains extremely long‐term cycling for 2407 h at 5 mA cm −2 with 5 mAh cm −2 and 1300 h at 10 mA cm −2 with 10 mAh cm −2 in Zn//Zn symmetrical cells. A high average CE of 99.3% is achieved over 430 cycles at 15% depth of discharge.